We evaluated the effects of rosiglitazone (4 mg b.i.d.) and metformin (1 g b.i.d.) monotherapy for 26 weeks on adipose tissue insulin-stimulated glucose uptake in patients (n = 41) with type 2 diabetes. Before and after the treatment, glucose uptake was measured using 2-[(18)F]fluoro-2-deoxyglucose and positron emission tomography and adipose tissue masses were quantified using magnetic resonance imaging. Rosiglitazone improved insulin-stimulated whole-body glucose uptake by 44% (P < 0.01 vs. placebo). Mean body weight was unchanged in the rosiglitazone group, while it decreased by 2.0 kg in the metformin group (P < 0.05 vs. placebo). In visceral adipose tissue, glucose uptake increased by 29% (from 17.8 +/- 2.0 to 23.0 +/- 2.6 micro mol x kg(-1) x min(-1), P < 0.05 vs. placebo) in the rosiglitazone group but to a lesser extent (17%) in the metformin group (from 16.2 +/- 1.5 to 18.9 +/- 1.7 micro mol x kg(-1) x min(-1), P < 0.05 vs. baseline). Because the visceral adipose tissue mass simultaneously decreased with both treatments (P < 0.05), no change was observed in total visceral glucose uptake per depot. Rosiglitazone significantly enhanced glucose uptake in the femoral subcutaneous area, either when expressed per tissue mass (from 10.8 +/- 1.2 to 17.1 +/- 1.7 micro mol x kg(-1) x min(-1), P < 0.01 vs. placebo) or per whole-fat depot (P < 0.05 vs. placebo). In conclusion, metformin treatment resulted in improvement of glycemic control without enhancement of peripheral insulin sensitivity. The improved insulin sensitivity of the nonabdominal subcutaneous adipose tissue during treatment with rosiglitazone partly explains the enhanced whole-body insulin sensitivity and underlies the central role of adipose tissue for action of peroxisome proliferator-activated receptor gamma agonist in vivo.

Ghrelin plasma concentrations increase during fasting and fall rapidly after nutrient ingestion. We hypothesized that insulin or glucose could regulate ghrelin secretion by a feedback mechanism. In this randomized, double-blind, placebo-controlled crossover study, three different study days were carried out in nine healthy volunteers (age 26 +/- 6 years). On each day, stepwise increasing systemic glucose concentrations of 5.0, 8.3, and 11.1 mmol/l were attained by intravenous infusion of glucose, representing fasting and postprandial conditions. Ghrelin plasma concentration was studied during concomitant exogenous hyperinsulinemia, inhibition of endogenous insulin production by somatostatin infusion, and placebo time control, respectively. Elevated glucose concentrations increased circulating insulin to 612 +/- 85 pmol/l (P < 0.01), but they did not affect ghrelin concentrations. Prolonged hyperinsulinemia by exogenous infusion resulted in circulating insulin of 1,602 +/- 261 pmol/l (P < 0.01) and suppressed plasma ghrelin to 49.6% of baseline (P < 0.01). During administration of somatostatin, insulin concentration remained constant, but an even greater decrease in ghrelin to 39.5% of baseline was noted (P < 0.01). Hyperglycemia does not decrease ghrelin, and a reduction in ghrelin is only seen at supraphysiological insulin concentrations. In contrast, systemic ghrelin concentrations are decreased by somatostatin. The meal-related suppression of ghrelin appears not directly regulated by glucose or insulin.

Rosiglitazone, a thiazolidinedione, enhances peripheral insulin sensitivity in patients with type 2 diabetes. Because the synergic action of insulin and exercise has been shown to be decreased in insulin resistance, the aim of this study was to compare the effects of rosiglitazone and metformin on muscle insulin responsiveness at rest and during exercise in patients with type 2 diabetes. Therefore, 45 patients with newly diagnosed or diet-treated type 2 diabetes were randomized for treatment with rosiglitazone (4 mg b.i.d.), metformin (1 g b.i.d.), or placebo in a 26-week double-blind trial. Skeletal muscle glucose uptake was measured using fluorine-18-labeled fluoro-deoxy-glucose and positron emission tomography (PET) during euglycemic-hyperinsulinemic clamp and one-legged exercise before and after the treatment period. Rosiglitazone (P < 0.05) and metformin (P < 0.0001) treatment lowered the mean glycosylated hemoglobin. The skeletal muscle glucose uptake was increased by 38% (P < 0.01) and whole-body glucose uptake by 44% in the rosiglitazone group. Furthermore, the exercise-induced increment during insulin stimulation was enhanced by 99% (P < 0.0001). No changes were observed in skeletal muscle or whole-body insulin sensitivity in the metformin group. In conclusion, rosiglitazone but not metformin 1) improves insulin responsiveness in resting skeletal muscle and 2) doubles the insulin-stimulated glucose uptake rate during physical exercise in patients with type 2 diabetes. Our results suggest that rosiglitazone improves synergic action of insulin and exercise.

We estimated glomerular cell number in 50 normotensive type 1 diabetic patients with raised albumin excretion rate (AER) and investigated any change after 3 years in a subgroup of 16 placebo-treated patients. Biopsies from 10 normal kidney donors were used as controls. Mesangial and endothelial cell number was increased in the 50 diabetic patients at the start of the study compared with control subjects. There was no difference in podocyte number. Glomerular volume was increased in diabetic patients, but surface area of glomerular basement membrane (GBM) underlying the podocytes did not differ between groups. AER correlated positively with mesangial cell number in microalbuminuric patients (r = 0.44, P = 0.012) and negatively with podocyte number in proteinuric patients (r = -0.48, P = 0.040). In the 16 placebo-treated patients, glomerular volume increased after 3 years owing to matrix accumulation and increased GBM surface area. Although overall cell number did not differ significantly from baseline, the decrease in podocyte number during follow-up correlated with AER at follow-up (r = -0.72, P = 0.002). In conclusion, cross-sectional analysis of podocyte number in type 1 diabetic patients with raised AER but normal blood pressure shows no significant reduction compared with nondiabetic control subjects. Longitudinal data provide evidence for an association between podocyte loss and AER, but whether cellular changes are a response to, a cause of, or concomitant with the progression of nephropathy remains uncertain.

Myocardial dysfunction, perfusion abnormalities, and the extent to which these abnormalities may be reversed by C-peptide administration was assessed in type 1 diabetic patients. Eight patients were studied before and during a 0.84-mg/kg dipyridamole administration using a randomized double-blind crossover protocol with infusion of C-peptide (6 pmol x kg(-1) x min(-1)) or saline during 60 min on two different days. Myocardial function was measured as peak myocardial velocity during systole (Vs) and early diastole (Vd) by pulsed tissue Doppler imaging. Myocardial contrast echocardiography was used for assessment of myocardial blood volume (SI(max)) and myocardial blood flow index (MBFI) calculated from the relation between trigger interval and signal intensity. Eight age-matched healthy volunteers served as control subjects. In the basal state, Vd (13.8 +/- 0.6 vs. 15.6 +/- 0.5 cm/s, P < 0.04) and SI(max) (6.6 +/- 0.6 vs. 8.2 +/- 0.6 a.u. P < 0.04) were reduced in patients compared with control subjects. Dipyridamole administration significantly increased indexes of myocardial function and blood flow to a similar extent in patients and control subjects. During C-peptide administration, Vs and Vd increased by 12% (P = 0.03), SI(max) increased from 6.6 +/- 0.6 to 8.1 +/- 0.7 a.u. (P < 0.02), and MBFI increased from 3.3 +/- 0.4 to 5.3 +/- 0.9 (P < 0.05). The results demonstrate that type 1 diabetic patients have impaired myocardial function and perfusion in the basal state that can be improved by short-term replacement of C-peptide.

Splanchnic glucose uptake (SGU) plays a major role in the disposal of an oral glucose load (OGL). To investigate the effect of an elevated plasma free fatty acid (FFA) concentration on SGU in patients with type 2 diabetes, we measured SGU in eight diabetic patients (mean age 51 +/- 4 years, BMI 29.3 +/- 1.4 kg/m(2), fasting plasma glucose 9.3 +/- 0.7 mmol/l) during an intravenous Intralipid/heparin infusion and 7-10 days later during a saline infusion. SGU was estimated by the OGL insulin clamp method: subjects received a 7-h euglycemic-hyperinsulinemic clamp (insulin infusion rate = 100 mU x m(-2) x min(-1)), and a 75-g OGL was ingested 3 h after starting the insulin clamp. After glucose ingestion, the steady-state glucose infusion rate during the insulin clamp was decreased appropriately to maintain euglycemia. SGU was calculated by subtracting the integrated decrease in glucose infusion rate during the 4-h period after glucose ingestion from the ingested glucose load (75 g). 3-[(3)H]glucose was infused during the 3-h insulin clamp before glucose ingestion to determine the rates of endogenous glucose production and glucose disappearance (R(d)). Intralipid/heparin or saline infusion was initiated 2 h before the start of the OGL clamp. Plasma FFA concentrations were significantly higher during the OGL clamp with the intralipid/heparin infusion than with the saline infusion (2.5 +/- 0.3 vs. 0.11 +/- 0.02 mmol/l, P < 0.001). During the 3-h insulin clamp period before glucose ingestion, Intralipid/heparin infusion reduced R(d) (4.4 +/- 0.3 vs. 5.3 +/- 0.3 mg x kg(-1) x min(-1), P < 0.01). During the 4-h period after glucose ingestion, SGU was significantly decreased during the intralipid/heparin versus saline infusion (30 +/- 2 vs. 37 +/- 2%, P < 0.01). In conclusion, an elevation in plasma FFA concentration impairs both peripheral and SGU in patients with type 2 diabetes.

Insulin resistance is frequently associated with increased lipid content in muscle and liver. Insulin excess stimulates tissue lipid accumulation. To examine the effects of insulin and improved glycemia on insulin sensitivity and intracellular lipids, we performed stepped (1, 2, and 4 mU x min(-1) x kg(-1)) hyperinsulinemic-euglycemic clamps in eight type 2 diabetic and six nondiabetic control subjects at baseline and after 12 and 67 h of insulin-mediated near-normoglycemia (118 +/- 7 mg/dl). Intrahepatocellular lipids (IHCLs) and intramyocellular lipids (IMCLs) of soleus (IMCL-S) and tibialis anterior muscle (IMCL-TA) were measured with (1)H nuclear magnetic resonance spectroscopy. At baseline, nondiabetic subjects had an approximate twofold higher insulin sensitivity (P < 0.02) and lower IHCLs than diabetic patients (5.8 +/- 1.2 vs. 18.3 +/- 4.2%, P < 0.03), in whom IMCL-TA negatively correlated with insulin sensitivity (r = -0.969, P < 0.001). After a 67-h insulin infusion in diabetic patients, IMCL-S and IHCLs were increased (P < 0.05) by approximately 36 and approximately 18%, respectively, and correlated positively with insulin sensitivity (IMCL-S: r = 0.982, P < 0.0005; IHCL: r = 0.865, P < 0.03), whereas fasting glucose production, measured with D-[6,6-(2)H(2)]glucose, decreased by approximately 10% (P < 0.04). In conclusion, these results indicate that IMCLs relate to insulin resistance in type 2 diabetic patients at baseline and that insulin-mediated near-normoglycemia for approximately 3 days reduces fasting glucose production but stimulates lipid accumulation in liver and muscle without affecting insulin sensitivity.

The insulin-sensitizing effects of thiazolidinediones are thought to be mediated through peroxisome proliferator-activated receptor-gamma, a nuclear receptor that is highly abundant in adipose tissue. It has been reported that adipocytes secrete a variety of proteins, including tumor necrosis factor-alpha, resistin, plasminogen activator inhibitor-1, and adiponectin. Adiponectin is a fat cell-secreted protein that has been reported to increase fat oxidation and improve insulin sensitivity. Our aim was to study the effects of troglitazone on adiponectin levels in lean, obese, and diabetic subjects. Ten diabetic and 17 nondiabetic subjects (8 lean, BMI <27 kg/m(2) and 9 obese, BMI >27 kg/m(2)) participated in the study. All subjects underwent an 80 mU. m(-2). min(-1) hyperinsulinemic-euglycemic glucose clamp before and after 3 months' treatment with the thiazolidinedione (TZD) troglitazone (600 mg/day). Fasting plasma glucose significantly decreased in the diabetic group after 12 weeks of treatment compared with baseline (9.1 +/- 0.9 vs. 11.1 +/- 0.9 mmol/l, P < 0.005) but was unchanged in the lean and obese subjects. Fasting insulin for the entire group was significantly lower than baseline (P = 0.02) after treatment. At baseline, glucose disposal rate (R(d)) was lower in the diabetic subjects (3.4 +/- 0.5 mg. kg(-1). min(-1)) than in the lean (12.3 +/- 0.4) or obese subjects (6.7 +/- 0.7) (P < 0.001 for both) and was significantly improved in the diabetic and obese groups (P < 0.05) after treatment, and it remained unchanged in the lean subjects. Baseline adiponectin levels were significantly lower in the diabetic than the lean subjects (9.0 +/- 1.7 vs. 16.7 +/- 2.7 micro g/ml, P = 0.03) and rose uniformly in all subjects (12.2 +/- 2.3 vs. 25.7 +/- 2.6 micro g/ml, P < 10(-4)) after treatment, with no significant difference detected among the three groups. During the glucose clamps, adiponectin levels were suppressed below basal levels in all groups (10.2 +/- 2.3 vs. 12.2 +/- 2.3 micro g/ml, P < 0.01). Adiponectin levels correlated with R(d) (r = 0.46, P = 0.016) and HDL cholesterol levels (r = 0.59, P < 0.001) and negatively correlated with fasting insulin (r = -0.39, P = 0.042) and plasma triglyceride (r = -0.61, P < 0.001). Our findings show that TZD treatment increased adiponectin levels in all subjects, including normal subjects in which no other effects of TZDs are observed. Insulin also appears to suppress adiponectin levels. We have confirmed these results in normal rats. These findings suggest that adiponectin can be regulated by obesity, diabetes, TZDs, and insulin, and it may play a physiologic role in enhancing insulin sensitivity.

Ghrelin is a novel enteric hormone that stimulates growth hormone (GH), ACTH, and epinephrine; augments plasma glucose; and increases food intake by inducing the feeling of hunger. These characteristics make ghrelin a potential counterregulatory hormone. At present, it is not known whether ghrelin increases in response to insulin-induced hypoglycemia. To answer this question, we compared plasma ghrelin concentrations after a short-term insulin infusion that was allowed or not (euglycemic clamp) to cause hypoglycemia (2.7 +/- 0.2 mmol/l at 30 min) in five healthy volunteers. In both studies, plasma ghrelin concentrations decreased (P < 0.01) after insulin infusion (hypoglycemia by 14%, euglycemia by 22%), reached a nadir at 30 min, and returned to baseline at 60 min, without differences between the hypoglycemia and the euglycemia studies. Glucagon, cortisol, and GH increased in response to hypoglycemia despite the decreased ghrelin. There was a strong correlation (R(2) = 0.91, P < 0.002) between the insulin sensitivity of the subjects and the percentage suppression of ghrelin from baseline. These data demonstrate that ghrelin is not required for the hormonal defenses against insulin-induced hypoglycemia and that insulin can suppress ghrelin levels in healthy humans. These results raise the possibility that postprandial hyperinsulinemia is responsible for the reduction of plasma ghrelin that occurs during meal intake.

Glucocorticoids induce insulin resistance in humans, whereas thiazolidinediones enhance insulin sensitivity. Although the effects of glucocorticoids and thiazolidinediones have been assessed in isolation, interaction between these drugs, which both act as ligands for nuclear receptors, has been less well studied. Therefore, we examined the metabolic effects of dexamethasone and troglitazone, alone and in combination, for the first time in humans. A total of 10 healthy individuals with normal glucose tolerance (age 40 +/- 11 years, BMI 31 +/- 6.1 kg/m(2)) were sequentially studied at baseline, after 4 days of dexamethasone (4 mg/day), after 4-6 weeks on troglitazone alone (400 mg/day), and again after 4 days of dexamethasone added to troglitazone. Key metabolic variables included glucose tolerance assessed by blood glucose and insulin responses to an oral glucose tolerance test (OGTT), insulin sensitivity evaluated via hyperinsulinemic-euglycemic clamp, free fatty acids (FFAs) and FFA suppressibility by insulin during the clamp study, and fasting serum leptin. Dexamethasone drastically impaired glucose tolerance, with fasting and 2-h OGTT insulin values increasing by 2.3-fold (P < 0.001) and 4.4-fold (P < 0.001) over baseline values, respectively. The glucocorticoid also induced a profound state of insulin resistance, with a 34% reduction in maximal glucose disposal rates (GDRs; P < 0.001). Troglitazone alone increased GDRs by 20% over baseline (P = 0.007) and completely prevented the deleterious effects of dexamethasone on glucose tolerance and insulin sensitivity, as illustrated by a return of OGTT glucose and insulin values and maximal GDR to near-baseline levels. Insulin-mediated FFA suppressibility (FFA decline at 30 min during clamp/FFA at time 0) was also markedly reduced by dexamethasone (P = 0.002). Troglitazone had no effect per se, but it was able to normalize FFA suppressibility in subjects coadministered dexamethasone. Futhermore, the magnitudes of response of FFA suppressibility and GDR to dexamethasone were proportionate. The same was true for the reversal of dexamethasone-induced insulin resistance by troglitazone, but not in response to troglitazone alone. Leptin levels were increased 2.2-fold above baseline by dexamethasone. Again, troglitazone had no effect per se but blocked the dexamethasone-induced increase in leptin. Subjects experienced a 1.7-kg weight gain while taking troglitazone but no other untoward effects. We conclude that in healthy humans, thiazolidinediones antagonize the action of dexamethasone with respect to multiple metabolic effects. Specifically, troglitazone reverses both glucocorticoid-induced insulin resistance and impairment of glucose tolerance, prevents dexamethasone from impairing the antilipolytic action of insulin, and blocks the increase in leptin levels induced by dexamethasone. Even though changes in FFA suppressibility were correlated with dexamethasone-induced insulin resistance and its reversal by troglitazone, a cause-and-effect relationship cannot be established. However, the data suggest that glucocorticoids and thiazolidinediones exert fundamentally antagonistic effects on human metabolism in both adipose and muscle tissues. By preventing or reversing insulin resistance, troglitazone may prove to be a valuable therapeutic agent in the difficult clinical task of controlling diabetes in patients receiving glucocorticoids.

Type 2 diabetes frequently results from progressive failure of pancreatic beta-cell function in the presence of chronic insulin resistance. We tested whether chronic amelioration of insulin resistance would preserve pancreatic beta-cell function and delay or prevent the onset of type 2 diabetes in high-risk Hispanic women. Women with previous gestational diabetes were randomized to placebo (n = 133) or the insulin-sensitizing drug troglitazone (400 mg/day; n = 133) administered in double-blind fashion. Fasting plasma glucose was measured every 3 months, and oral glucose tolerance tests (OGTTs) were performed annually to detect diabetes. Intravenous glucose tolerance tests (IVGTTs) were performed at baseline and 3 months later to identify early metabolic changes associated with any protection from diabetes. Women who did not develop diabetes during the trial returned for OGTTs and IVGTTs 8 months after study medications were stopped. During a median follow-up of 30 months on blinded medication, average annual diabetes incidence rates in the 236 women who returned for at least one follow-up visit were 12.1 and 5.4% in women assigned to placebo and troglitazone, respectively (P < 0.01). Protection from diabetes in the troglitazone group 1) was closely related to the degree of reduction in endogenous insulin requirements 3 months after randomization, 2) persisted 8 months after study medications were stopped, and 3) was associated with preservation of beta-cell compensation for insulin resistance. Treatment with troglitazone delayed or prevented the onset of type 2 diabetes in high-risk Hispanic women. The protective effect was associated with the preservation of pancreatic beta-cell function and appeared to be mediated by a reduction in the secretory demands placed on beta-cells by chronic insulin resistance.

We investigated whether the effect of troglitazone on glucose disposal is associated with altered insulin signaling. Nondiabetic first-degree relatives of type 2 diabetic patients (age 30 +/- 2 years, BMI 30 +/- 1 kg/m(2); n = 20) were randomized in a double-blind manner to 3 months of troglitazone (200 mg/day) or placebo treatment. Before and after treatment, 3-h euglycemic-hyperinsulinemic glucose clamps (40 mU. m(-2). min(-1)) were performed, and muscle biopsies were obtained immediately before and after the clamps. In the biopsies, insulin receptor kinase (IRK) activity, insulin receptor substrate (IRS)-1-associated phosphatidylinositol 3-kinase (PI3K) activity, Ser(473) and Thr(308) phosphorylation of protein kinase B (PKB), and protein expression of IRS-1, IRS-2, phosphoinositol-dependent kinase-1 (PDK-1), PKB, and GLUT-4 were determined. After troglitazone treatment, insulin-stimulated glucose disposal was increased compared with pretreatment and placebo (279 +/- 37 vs. 211 +/- 26 and 200 +/- 25 mg. m(-2). min(-1); both P < 0.05). IRK and PI3K activities were not altered by troglitazone, but PKB Ser(473) phosphorylation was enhanced compared with pretreatment and placebo at the clamp insulin level (138 +/- 36 vs. 77 +/- 16 and 55 +/- 13 internal standard units; both P < 0.05) and with pretreatment at the basal level (31 +/- 9 vs. 14 +/- 4 internal standard units; P < 0.05). PKB Thr(308) phosphorylation also tended to be higher, but this was not statistically significant. Troglitazone did not alter insulin receptor number or IRS-1, IRS-2, PKB, PDK-1, or GLUT-4 protein expression. We conclude that increased PKB phosphorylation may contribute to the insulin-sensitizing effects of thiazolidinediones in human skeletal muscle.

In a double-blind, placebo-controlled, randomized crossover study, 15 stable mild hyperglycemic patients without treatment and with features of metabolic syndrome were treated with cerivastatin (0.4 mg/day) or placebo for 3 months. The insulin sensitivity index during the euglycemic-hyperinsulinemic clamp (EHC; 5.4 mmol/l; 80 mU x m(-2) x min(-1)) was increased by cerivastatin treatment (66.39 +/- 3.9 nmol x lean body mass [LBM](-1) x min(-1) x pmol(-1) x l(-1)) as compared with placebo (58.37 +/- 3.69 nmol x LBM(-1) x min(-1) x pmol(-1) x l(- 1); P < 0.01) by 13.7%. Glucose oxidation during EHC was significantly higher with statin treatment (16.1 +/- 1.37 micromol x LBM(-1) x min(-1)) as compared with placebo (14.58 +/- 1.48 micromol x LBM(-1) x min(-1); P < 0.05). During hyperinsulinemia (approximately 800 pmol/l) in EHC steady-state, lipid oxidation was significantly decreased and respiratory quotient was significantly increased with statin treatment (0.33 +/- 0.05 mg x LBM(-1) x min(- 1), 0.94 +/- 0.01) as compared with placebo (0.48 +/- 0.06 mg x LBM(-1) x min(-1), 0.91 +/- 0.01; P < 0.01 and P < 0.05, respectively). During statin treatment, the first-phase insulin response increased from 2.07 +/- 0.28 to 2.82 +/- 0.38 pmol x l(-1) x pmol(-1) (P < 0.05). The second phase of insulin responses examined by C-peptide and insulin levels averaged during the hyperglycemic clamp (20 mmol/l) was unchanged. In conclusion, this study demonstrates that 0.4 mg cerivastatin therapy improves first-phase insulin secretion and increases insulin-mediated glucose uptake and respiratory quotient in the early state of obese type 2 diabetes.

The association of the Pro12Ala polymorphism of the PPAR-gamma2 gene with the incidence of type 2 diabetes was investigated in 522 subjects with impaired glucose tolerance (IGT) participating in the Finnish Diabetes Prevention Study. Subjects were randomized to either an intensive diet and exercise group or a control group. By 3 years of intervention, the odds ratio of the development of type 2 diabetes for subjects with the Ala12 allele was 2.11-fold compared with that for subjects with the Pro12Pro genotype (95% CI 1.20-3.72). The risk for type 2 diabetes increased also in subjects who gained weight or belonged to the control group. In the intervention group, subjects with the Ala12Ala genotype lost more weight during the follow-up than subjects with other genotypes (Pro12Pro vs. Ala12Ala P = 0.043), and none of subjects with the Ala12Ala genotype developed type 2 diabetes in this group. In conclusion, the Ala12 allele may predispose to the development of type 2 diabetes in obese subjects with IGT. However, beneficial changes in diet, increases in physical activity, and weight loss may reverse, to some extent, the diabetogenic impact of the Ala12 allele, possibly due to an improved insulin sensitivity.

Nitric oxide (NO) synthase inhibition reduces leg glucose uptake during cycling without reducing leg blood flow (LBF) in young, healthy individuals. This study sought to determine the role of NO in glucose uptake during exercise in individuals with type 2 diabetes. Nine men with type 2 diabetes and nine control subjects matched for age, sex, peak pulmonary oxygen uptake (VO(2) peak), and weight completed two 25-min bouts of cycling exercise at 60 +/- 2% VO(2) peak, separated by 90 min. N(G)-monomethyl-L-arginine (L-NMMA) (total dose 6 mg/kg) or placebo was administered into the femoral artery for the final 15 min of exercise in a counterbalanced, blinded, crossover design. LBF was measured by thermodilution in the femoral vein, and leg glucose uptake was calculated as the product of LBF and femoral arteriovenous glucose difference. During exercise with placebo, glucose uptake was not different between control subjects and individuals with diabetes; however, LBF was lower and arterial plasma glucose and insulin levels were higher in individuals with diabetes. L-NMMA had no effect on LBF or arterial plasma glucose and insulin concentrations during exercise in both groups. L-NMMA significantly reduced leg glucose uptake in both groups, with a significantly greater reduction (P = 0.04) in the diabetic group (75 +/- 13%, 5 min after L-NMMA) compared with the control group (34 +/- 14%, 5 min after L-NMMA). These data suggest a greater reliance on NO for glucose uptake during exercise in individuals with type 2 diabetes compared with control subjects.

Hepatic accumulation of lipid substrates perturbs apolipoproteinB-100 (apoB) metabolism in insulin-resistant, obese subjects and may account for increased risk of cardiovascular disease. In a placebo-controlled trial, we examined the independent and combined effects of decreasing cholesterol synthesis with atorvastatin (40 mg/day) and triglyceride synthesis with fish oils (4 g/day) on apoB kinetics. The subjects were 48 viscerally obese, insulin-resistant men with dyslipidemia who were studied in a fasted state. We found that atorvastatin significantly decreased plasma apoB-containing lipoproteins (P < 0.001, main effect) through increases in the fractional catabolic rate (FCR) of VLDL-, IDL-, and LDL-apoB (P < 0.01). Fish oils significantly decreased plasma levels of triglycerides and VLDL-apoB (P < 0.001), decreased the VLDL-apoB secretion rate (P < 0.01), but increased the conversion of VLDL to LDL (P < 0.001). Compared with placebo, combined treatment with atorvastatin and fish oils decreased VLDL-apoB secretion (P < 0.03) and increased the FCR of apoB in each lipoprotein fraction (P < 0.03) and the percent conversion of VLDL to LDL (P < 0.05). None of the treatments altered insulin resistance. In conclusion, in visceral obesity, atorvastatin increased hepatic clearance of all apoB-containing lipoproteins, whereas fish oils decreased hepatic secretion of VLDL-apoB. The differential effects of atorvastatin and fish oils on apoB kinetics support their combined use in correcting defective apoB metabolism in obese, insulin-resistant subjects.

Metformin is an effective hypoglycemic drug that lowers blood glucose concentrations by decreasing hepatic glucose production and increasing glucose disposal in skeletal muscle; however, the molecular site of metformin action is not well understood. AMP-activated protein kinase (AMPK) activity increases in response to depletion of cellular energy stores, and this enzyme has been implicated in the stimulation of glucose uptake into skeletal muscle and the inhibition of liver gluconeogenesis. We recently reported that AMPK is activated by metformin in cultured rat hepatocytes, mediating the inhibitory effects of the drug on hepatic glucose production. In the present study, we evaluated whether therapeutic doses of metformin increase AMPK activity in vivo in subjects with type 2 diabetes. Metformin treatment for 10 weeks significantly increased AMPK alpha2 activity in the skeletal muscle, and this was associated with increased phosphorylation of AMPK on Thr172 and decreased acetyl-CoA carboxylase-2 activity. The increase in AMPK alpha2 activity was likely due to a change in muscle energy status because ATP and phosphocreatine concentrations were lower after metformin treatment. Metformin-induced increases in AMPK activity were associated with higher rates of glucose disposal and muscle glycogen concentrations. These findings suggest that the metabolic effects of metformin in subjects with type 2 diabetes may be mediated by the activation of AMPK alpha2.

Type 2 diabetes is characterized by muscle insulin resistance. Nondiabetic first-degree relatives of type 2 diabetic patients have also been reported to have insulin resistance. A polygenic basis for pathogenesis of type 2 diabetes has been proposed. A gene expression profile was evaluated in the skeletal muscle of patients with type 2 diabetes while not on treatment for 2 weeks and after 10 days of intensive insulin treatment. Comparison of gene expression pattern with age-, sex-, and BMI-matched people with no family history of diabetes was performed using a microarray technique (Hu6800 arrays; Affymetrix, Santa Clara, CA). Only those gene transcripts showing > or =1.9-fold changes and an average difference in fluorescence intensity of > or =1,000 in all subjects are reported. Insulin sensitivity (SI) was measured using an intravenous glucose tolerance test. Of 6,451 genes surveyed, transcriptional patterns of 85 genes showed alterations in the diabetic patients after withdrawal of treatment, when compared with patterns in the nondiabetic control subjects. Insulin treatment reduced the difference in patterns between diabetic and nondiabetic control subjects (improved) in all but 11 gene transcripts, which included genes involved in structural and contractile functions, growth and tissue development, stress response, and energy metabolism. These improved transcripts included genes involved in insulin signaling, transcription factors, and mitochondrial maintenance. However, insulin treatment altered the transcription of 29 additional genes involved in signal transduction; structural and contractile functions; growth and tissue development; and protein, fat, and energy metabolism. Type 2 diabetic patients had elevated circulating insulin during the insulin-treated phase, although their blood glucose levels (98.8 +/- 6.4 vs. 90.0 +/- 2.9 mg/dl for diabetic vs. control) were similar to those of the control subjects. In contrast, after withdrawal of treatment, the diabetic patients had reduced SI and elevated blood glucose (224.0 +/- 26.2 mg/dl), although their insulin levels were similar to those of the nondiabetic control subjects. This study identified several candidate genes for muscle insulin resistance, complications associated with poor glycemic control, and effects of insulin treatment in people with type 2 diabetes.

It has been proposed that insulin-mediated changes in muscle perfusion modulate insulin-mediated glucose uptake. However, the putative effects of insulin on the microcirculation that permit such modulation have not been studied in humans. We examined the effects of systemic hyperinsulinemia on skin microvascular function in eight healthy nondiabetic subjects. In addition, the effects of locally administered insulin on skin blood flow were assessed in 10 healthy subjects. During a hyperinsulinemic clamp, we measured leg blood flow with venous occlusion plethysmography, skin capillary density with capillaroscopy, endothelium-(in)dependent vasodilatation of skin microcirculation with iontophoresis of acetylcholine and sodium nitroprusside combined with laser Doppler fluxmetry, and skin vasomotion by Fourier analysis of microcirculatory blood flow. To exclude nonspecific changes in the hemodynamic variables, a time-volume control study was performed. Insulin iontophoresis was used to study the local effects of insulin on skin blood flow. Compared to the control study, systemic hyperinsulinemia caused an increase in leg blood flow (-0.54 +/- 0.93 vs. 1.97 +/- 1.1 ml. min(-1). dl(-1); P < 0.01), an increase in the number of perfused capillaries in the resting state (-3.7 +/- 3.0 vs. 3.4 +/- 1.4 per mm(2); P < 0.001) and during postocclusive reactive hyperemia (-0.8 +/- 2.2 vs. 5.1 +/- 3.7 per mm(2); P < 0.001), an augmentation of the vasodilatation caused by acetylcholine (722 +/- 206 vs. 989 +/- 495%; P < 0.05) and sodium nitroprusside (618 +/- 159 vs. 788 +/- 276%; P < 0.05), and a change in vasomotion by increasing the relative contribution of the 0.01- to 0.02-Hz and 0.4- to 1.6-Hz spectral components (P < 0.05). Compared to the control substance, locally administered insulin caused a rapid increase ( approximately 13.5 min) in skin microcirculatory blood flow (34.4 +/- 42.5 vs. 82.8 +/- 85.7%; P < 0.05). In conclusion, systemic hyperinsulinemia in skin 1) induces recruitment of capillaries, 2) augments nitric oxide-mediated vasodilatation, and 3) influences vasomotion. In addition, locally administered insulin 4) induces a rapid increase in total skin blood flow, independent of systemic effects.

Hypoglycemia-associated autonomic failure (HAAF)-reduced autonomic (including adrenomedullary epinephrine) and symptomatic responses to hypoglycemia caused by recent antecedent hypoglycemia-plays a key role in the pathogenesis of defective glucose counterregulation and hypoglycemia unawareness and thus iatrogenic hypoglycemia in type 1 diabetes. On the basis of the findings that cortisol infusion mimics and deficient or inhibited cortisol secretion minimizes this phenomenon, it has been suggested that the cortisol response to antecedent hypoglycemia mediates HAAF. We tested the hypothesis that any stimulus that releases cortisol, such as exercise, reduces autonomic and symptomatic responses to subsequent hypoglycemia. Thirteen healthy young adults (four women) were studied on three occasions in random sequence: 1) cycle exercise ( approximately 70% peak oxygen consumption) from 0830 to 0930 h and from 1200 to 1300 h on day 1 and hyperinsulinemic (2.0 mU x kg(-1) x min(-1)) stepped hypoglycemic (85, 75, 65, 55, and 45 mg/dl) clamps on day 2, 2) rest on day 1 and identical hypoglycemic clamps on day 2, and 3) hyperinsulinemic-euglycemic clamps. Exercise raised plasma cortisol concentrations to 16.9 +/- 1.9 (0930 h) and 16.6 +/- 1.6 microg/dl (1300 h) on day 1. Compared with rest on day 1, exercise on day 1 was associated with reduced epinephrine (P = 0.0113) responses-but not norepinephrine (P = 0.6270), neurogenic symptom (P = 0.6470), pancreatic polypeptide (P = 0.0629), or glucagon (P = 0.0436, but higher) responses-to hypoglycemia on day 2. However, the effect was small. (The final day 2 hypoglycemia epinephrine values were 765 +/- 106 pg/ml after rest on day 1 and 550 +/- 94 pg/ml after exercise on day 1 compared with 30 +/- 6 pg/ml during euglycemia.) These data are consistent with the hypothesis that the cortisol response to hypoglycemia mediates in part the reduced epinephrine response to subsequent hypoglycemia, one key component of HAAF in type 1 diabetes. However, the small effect suggests that an additional factor or factors may well be involved. These data do not support the hypothesis that the cortisol response to hypoglycemia mediates the reduced neurogenic symptom response to subsequent hypoglycemia, another key component of HAAF in type 1 diabetes.